Marijuana research: Is the limit for stoned-while-driving too high?

By JAKE ELLISON, SEATTLEPI.COM STAFF

Updated 7:27 am, Wednesday, January 30, 2013

Some marijuana users continue to complain that Washington's new pot law creating a 5-nanograms-per-milliliter limit for active THC is too low of a DUI standard and that having a standard at all will unjustly criminalize medical marijuana users.

Well, they are in for some bad news.

Not only is the limit for a "per se" charge of driving under the influence in Washington not too low, but it might be too high to capture impaired drivers, according to recently released research conducted by a group in the National Institutes of Health.

Another study suggests driving by heavy users is impaired nearly a month after their most recent puff of cannabis. Oh, and, a companion study suggests marijuana may in fact be addictive ...

Medical marijuana patients Brett Skaret, 20, left, and Joe Engelhardt, 22, enjoy the freedom of a smoking room with other smokers Saturday, December 8, 2012, at the NW Cannabis Market in Seattle, Washington. The pair are vehemently opposed to the recent passage of I-502. "The whole thing criminalizes patients," Skaret said. "It's all for the money." (JORDAN STEAD/SPECIAL TO THE CHRONICLE)

Inspired by victorious measures to legalize marijuana in Colorado and Washington, California activists are readying a new ballot push to expand legalization in the Golden State – but not until 2016, reports the Oregonian. In this photo, U.S. Rep. Earl Blumenauer, right, speaks during a town hall meeting on legalizing marijuana on Sunday in Portland, Ore. (AP Photo/The Oregonian, Brent Wojahn)

Inspired by victorious measures to legalize marijuana in Colorado and Washington, California activists are readying a new ballot push to expand legalization in the Golden State – but not until 2016, reports

This is the top of a study emailed to us under the subject line "They Lied." The author of the email wrote: "We proved, on several ocassions, that the science proved that the spokemen for New Approach Washington were lying. Active THC can stay in your blood for 30 days or more. They had zero science saying that the THC level would drop below 5ng in "a few hours". They got caught in the lie, but kept telling it anyway."

However, the study sent to us found active THC in the blood plasma, not in "whole blood" tests, the kind that will be performed for DUI charges in Washington. Plasma retains nearly double the amount of THC than whole blood, the study author said.

Looking at the above graph, from the research paper "Do D9-tetrahydrocannabinol concentrations indicate recent use in chronic cannabis users?" can lead to confusion in the debate over how long THC stays in the blood and whether 5 nanograms per mil is too low or high an amount that can lead to a DUI charge. The bottom part of the graph appears to show significant amounts of THC in the blood after 7 days. However, what's shown is the amount of THCCOOH - the inactive residue of THC.

Active THC, or its immediate derivative, the "equipotent monohydroxy compound," or "11-hydroxy-THC" or "11-OH-THC" – the active elements of marijuana that make you high – while not completely gone within hours of getting high, fall below the 5-nanogram limit within 24 hours.

For future reference, "THCCOOH" is the non-active residue of pot in the system, which sticks around a lot longer than active THC.

"With whole blood (testing), we haven't had anybody over five after 24 hours," said one of the nation's leading researchers on marijuana and its effects on people, with dozens of research papers under her belt.

Marilyn Huestis is a senior investigator in chemistry and drug metabolism at the Intramural Research Program under the National Institute on Drug Abuse and, thus, the National Institute of Health.

She added that almost no one tested at 5 nanograms of active THC after just a few hours, but she uses the 24-hour window just to round it all off. These results come from her group's most recent study released Jan. 2.

"A good proportion of even chronic daily users will be negative within the 24 hours and the remaining 15 (in the study) all were negative within three days except for seven people," who tested well below 5 nanograms at 30 days.

Again, that's "negative," not just under 5 nanograms.

Blood, not plasma

The first thing Huestis pointed out during her interview with us is that one of her studies used to argue against the 5-nanogram limit was a study done using plasma, the fluid part of blood that doesn't include red blood cells.

"THC doesn't get into red blood cells well at all," she said. And THC concentration in "plasma is about twice of what whole blood concentration is."

"THC and THCCOOH can be detected in plasma for up to 30 days of monitored abstinence in chronic daily cannabis smokers." The study also showed higher levels of active THC in later time frames than just a few hours ...

But, none of that counts, because that's not the testing law enforcement will conduct – they do whole blood testing and not plasma testing.

Too high of a limit?

"The level of 5 nanograms per mil is pretty high," Huestis said. "We know that people are impaired at lower levels than 5, but the balancing act is trying to find a number that can reliably separate (the impaired from the not-impaired), which is almost impossible to do."

In a pair of studies published in the past year, Huestis' team found two troublesome results.

And, two, heavy users in the second study, when compared to occasional users at 7, 14 and 21 days of abstinence, showed "psychomotor impairment that shows they'd have a hard time driving."

"They showed some small improvement," she said. "but they were significantly impaired three weeks after use."

Here's the deal

There are receptors in our head that react to cannabinoids or THC substances and the more you smoke the more these shut down, affecting memory, divided attention abilities, using sensory information with appropriate responses and, of course, hunger.

"This is the first time that we've shown that there's really a brain change with chronic cannabis use," she said.

And, apparently, those effects continue to challenge even a sober person's ability to drive. Although, with sustained abstinence, one can return eventually to normal performance because the brain does readjust to the absence of THC.

Wait, addictive?

These cannabinoid receptors are "not there just to enjoy marijuana," she said. "The brain is doing a lot with cannabinoids. When you smoke marijuana, you hijack what the normal brain is doing."

After ~4 weeks of continuously monitored abstinence from cannabis on a secure research unit, CB1 receptor density returned to normal levels. This is the first direct demonstration of cortical cannabinoid CB1 receptor downregulation as a neuroadaptation that may promote cannabis dependence in human brain.

Chronic cannabis smoking can lead to tolerance and withdrawal symptoms, the two hallmarks of dependence.

"It's showing that along with these THC concentrations in the blood, we have changes in the brain, and we have changes in (users') ability to perform these tasks."

When asked if she would recommend a lower active THC level for DUI laws based on her studies, Huestis said she doesn't comment on policy. Instead, she lets her research do the talking.